Comments

If you're running Windows in VirtualBox Windows is no longer directly correct to the soundcard in your actual computer but rather the virtual one that is VirtualBox. So installing the Windows drivers for your actual sound card in your VirtualBox will not help.

The speakers does not matter them either.

I presume that you are running Ubuntu 9.04 as your host OS, the operating system that you have installed on your actual computer. Are you trying to install the Windows drivers in Linux? Because that will not work.

I've been googling around the net for you which is what you should have done. But I found a page that people with your soundcard have been fallowing to sort out their sound issues.
Here you go and remember to up my karma if it works ^^.
http://www.ubuntugeek.com/sound-solutions-for-ubuntu-904-jaunty-users.html